I believe that the biggest changes are in the digital/electronic components and speakers.
Electronics like CD players, DACs, and digital preamps experience the most changes as digital technology keeps changing. They will also lose the most value as a result. And come to think of it CD Players are actually becoming obsolete as more folks go the streaming route!
Speakers have experienced a fair amount of changes and will likely continue to do so. Speaker manufactures push for new shapes/designs and use of new materials (graphene anyone?). Yet, even for speakers, don't expect a major change from a mark I to a mark II, despite what manufacturers want you to believe. If the changes were so drastic, they would have called it something else!
Amplifiers, analog preamps, and turntables are likely to experience the least amount of changes (Linn has been selling the LP12 for 40 years!). A good amp is a good amp, physics has not changed!
There is a lot of hype in this hobby. Customers just need to be aware.